Technical Field
The present invention relates to a DC-DC converter including a boosting chopper circuit, and particularly relates to a DC-DC converter having a function for protection during short circuit faults occurring in a semiconductor switching element.
Background Art
FIG. 17 illustrates a boosting chopper circuit disclosed in Patent Document 1.
In FIG. 17, IN1 and IN2 represent positive and negative input terminals connected to a DC power source (not shown), OUT1 and OUT2 represent positive and negative output terminals, L1 represents a reactor, Q1 and Q2 represent transistors, D1 and D2 represent diodes, and C1 and C2 represent capacitors. Note that there are cases where in addition to the reactor L1, another reactor is inserted between the negative-side input terminal IN2 and an emitter of the transistor Q2.
An outline of operations according to this conventional technique will be given next.
By turning both the transistors Q1 and Q2 on, a current flows from the DC power source in a path of the input terminal IN1→reactor L1→transistors Q1 and Q2→input terminal IN2, and energy is accumulated in the reactor L1. Next, by turning the transistor Q2 off while keeping the transistor Q1 on, the DC power source and energy accumulated in the reactor L1 are supplied along a path of the transistor Q1→capacitor C2→diode D2→input terminal IN2, which charges the capacitor C2.
Next, by turning the transistor Q1 off and turning the transistor Q2 on, a current flows in a path of the input terminal IN1→reactor L1→diode D1→capacitor C1→transistor Q2→input terminal IN2, which charges the capacitor C1. In this state, when the transistor Q2 is turned off, the DC power source and the energy accumulated in the reactor L1 are supplied along a path of the diode D1→capacitor C1→capacitor C2→diode D2, which charges the capacitors C1 and C2.
By repeating the above-described operations, a voltage between the output terminals OUT1 and OUT2 is boosted to a higher voltage than the voltage of the DC power source. An output voltage of this boosting chopper circuit can take on three levels, namely a voltage at the capacitor C1, a voltage at the capacitor C2, and a sum of the voltages at the capacitors C1 and C2, and thus is also called a three-level boosting chopper circuit.
When configuring a DC-DC converter using such a boosting chopper circuit, a circuit breaker that cuts off the DC power source during circuit faults, a control circuit for controlling the transistors Q1 and Q2 and the circuit breaker, and the like, which are not illustrated here, are generally provided as well.